A digital buffer is an electronic circuit that increases the driving capability of a digital signal. The buffer output follows the digital state of the input. This means that the buffer output is low when the input is low and high when the input is high.
Digital outputs are often utilized in industrial process control and automation systems, and typically make use of, for example, multi-channel 24V digital outputs modules with a limited output drive capability. Many of these outputs have line-monitoring features that include lead-breakage and short-circuit detection in the field wiring and load. A variety of field loads may have a large (e.g., “in-rush”) current. These field loads require a buffer. Usually that buffer will disable the line monitoring features of the output.